Squash Docker image to remove unnecessary layers in case you do not have a need to keep them.
Install docker-squash.
$ pip install docker-squash
Display help information.
$ docker-squash --help
usage: docker-squash [-h] [-v] [--version] [-d] [-f FROM_LAYER] [-t TAG] [-c] [--tmp-dir TMP_DIR] [--output-path OUTPUT_PATH] image
Docker layer squashing tool
positional arguments:
image Image to be squashed
optional arguments:
-h, --help show this help message and exit
-v, --verbose Verbose output
--version Show version and exit
-d, --development Does not clean up after failure for easier debugging
-f FROM_LAYER, --from-layer FROM_LAYER
ID of the layer or image ID or image name. If not specified will squash all layers in the image
-t TAG, --tag TAG Specify the tag to be used for the new image. If not specified no tag will be applied
-c, --cleanup Remove source image from Docker after squashing
--tmp-dir TMP_DIR Temporary directory to be created and used
--output-path OUTPUT_PATH
Path where the image should be stored after squashing. If not provided, image will be loaded into Docker
daemon
Inspect our sample DokuWiki image that will be used in this example.
$ docker image ls dokuwiki:latest
REPOSITORY TAG IMAGE ID CREATED SIZE dokuwiki latest 81fa953242ea 32 hours ago 51.2MB
$ docker history dokuwiki:latest
IMAGE CREATED CREATED BY SIZE COMMENT 81fa953242ea 32 hours ago /bin/sh -c #(nop) CMD ["unitd" "--no-daemon… 0B aad5ffa6cd31 32 hours ago /bin/sh -c #(nop) WORKDIR /opt/dokuwiki 0B a98a1806e8ec 32 hours ago /bin/sh -c #(nop) USER dokuwiki 0B cbe7109019c4 32 hours ago /bin/sh -c #(nop) EXPOSE 8080 0B e58156317f72 32 hours ago |2 GID=5000 UID=5000 /bin/sh -c chown -R dok… 672B 162700362dc1 32 hours ago /bin/sh -c #(nop) COPY file:25cd54fde2f41817… 672B 86190f8bf11d 32 hours ago /bin/sh -c #(nop) COPY file:c44cf51c56219ee0… 366B e675b4d5cd31 32 hours ago /bin/sh -c #(nop) COPY file:8f17ce87a068c7b4… 172B 311cba329257 32 hours ago /bin/sh -c #(nop) COPY file:a18b36cd71c66d32… 327B 5f266a479729 32 hours ago /bin/sh -c #(nop) COPY file:47074ff4abd6297f… 228B d8239e54107a 32 hours ago |2 GID=5000 UID=5000 /bin/sh -c apk add --no… 16.9MB 9bda04b7bdec 32 hours ago |2 GID=5000 UID=5000 /bin/sh -c apk add --no… 14.3MB feb2d2025277 32 hours ago /bin/sh -c #(nop) COPY dir:fb9054dc9d2ccd9af… 14.3MB 92a7fd2f9644 32 hours ago /bin/sh -c #(nop) LABEL application=Dokuwiki 0B 02390e6d72a2 32 hours ago /bin/sh -c #(nop) LABEL build_date= 0B 0403cc96ee02 32 hours ago /bin/sh -c #(nop) LABEL maintainer=Milosz G… 0B ab011b78698c 32 hours ago /bin/sh -c #(nop) ARG BUILD_DATE 0B b106775f33c9 32 hours ago /bin/sh -c #(nop) ARG GID=5000 0B 48a608d4aec2 32 hours ago /bin/sh -c #(nop) ARG UID=5000 0B 14119a10abf4 13 days ago /bin/sh -c #(nop) CMD ["/bin/sh"] 0B <missing> 13 days ago /bin/sh -c #(nop) ADD file:aad4290d27580cc1a… 5.6MB
Squash all layers and tag the new image.
$ docker-squash --tag dokuwiki:squashed dokuwiki:latest
2021-09-10 08:37:47,291 root INFO docker-squash version 1.0.8, Docker 75249d8, API 1.41... 2021-09-10 08:37:47,291 root INFO Using v2 image format 2021-09-10 08:37:47,297 root INFO Old image has 21 layers 2021-09-10 08:37:47,298 root INFO Checking if squashing is necessary... 2021-09-10 08:37:47,298 root INFO Attempting to squash last 21 layers... 2021-09-10 08:37:47,298 root INFO Saving image sha256:81fa953242eac0c98f35d5400e5921be0d83981e0280b37d09fcfbc9145d1a58 to /tmp/docker-squash-6e276eur/old directory... 2021-09-10 08:37:48,160 root INFO Image saved! 2021-09-10 08:37:48,161 root INFO Squashing image 'dokuwiki:latest'... 2021-09-10 08:37:48,161 root INFO Starting squashing... 2021-09-10 08:37:48,161 root INFO Squashing file '/tmp/docker-squash-6e276eur/old/70a2035b0eef207d0c40d3b06b3e67f69a97a52b67398b31262a39bbe4b30043/layer.tar'... 2021-09-10 08:37:48,163 root INFO Squashing file '/tmp/docker-squash-6e276eur/old/eabb7e8485249875a46a6e310a0a8efaae9481b0749648c33167d7378df9ad62/layer.tar'... 2021-09-10 08:37:48,163 root INFO Squashing file '/tmp/docker-squash-6e276eur/old/13e58f6558c933cab47f2453763a86db042fe1fe39091d5da303f46abfbe1818/layer.tar'... 2021-09-10 08:37:48,164 root INFO Squashing file '/tmp/docker-squash-6e276eur/old/cfebac32493419e94a16ae0980c5319bcf6b1279c26d095017ee38b6dbad9cd9/layer.tar'... 2021-09-10 08:37:48,164 root INFO Squashing file '/tmp/docker-squash-6e276eur/old/e23937289f7323fbbd4c0d3a49a83e07caa1e19ab87e0a9cc601b6095767ae39/layer.tar'... 2021-09-10 08:37:48,165 root INFO Squashing file '/tmp/docker-squash-6e276eur/old/d67fd73b1b4dabf8e354855661bdfd111e8db71d197750cbc57c4f6a8ee3b161/layer.tar'... 2021-09-10 08:37:48,165 root INFO Squashing file '/tmp/docker-squash-6e276eur/old/3bb511c620d893a55d29914ca10e0d2b00a7fac7914d4fcf6353f37c440d421a/layer.tar'... 2021-09-10 08:37:48,225 root INFO Squashing file '/tmp/docker-squash-6e276eur/old/eeb4ab19d86bc7fdaf6959f899da2d8d4a0c1570e8dd062b22a503344cb61e2c/layer.tar'... 2021-09-10 08:37:49,086 root INFO Squashing file '/tmp/docker-squash-6e276eur/old/1951918a94180fd1570e050a251a4a4e61883fb8e7d35cdd2c62aa0a6bf35f9b/layer.tar'... 2021-09-10 08:37:49,456 root INFO Squashing file '/tmp/docker-squash-6e276eur/old/5dee72d2797c533813effb8e9de26377300d29f418ebb06bfe814f950a7aa02b/layer.tar'... 2021-09-10 08:37:49,571 root INFO Squashing finished! 2021-09-10 08:37:49,702 root INFO Original image size: 57.36 MB 2021-09-10 08:37:49,702 root INFO Squashed image size: 39.64 MB 2021-09-10 08:37:49,702 root INFO Image size decreased by 30.88 % 2021-09-10 08:37:49,702 root INFO New squashed image ID is 3f89c7a43637b1c3e60186252371d6d653ddbcfb03b3c648adde8942050a9c50 2021-09-10 08:37:49,816 root INFO Image registered in Docker daemon as dokuwiki:squashed 2021-09-10 08:37:49,823 root INFO Done
Inspect squashed image.
$ docker image ls dokuwiki:squashed
REPOSITORY TAG IMAGE ID CREATED SIZE dokuwiki squashed 3f89c7a43637 18 seconds ago 36.8MB
$ docker history dokuwiki:squashed
IMAGE CREATED CREATED BY SIZE COMMENT 3f89c7a43637 31 seconds ago 36.8MB
Additional notes
Check out docker-squash source code.